seifert@ihuxl.UUCP (D.A. Seifert) (08/09/84)
> Processing a fixed IF signal is less expensive than many RF signals so it > is best (read cheaper) for TV designers to mix the RF and LO as close to the > antenna input as possible. Some of the LO signal may be coupled into the > antenna leads and then broadcast out the antenna. It is not very strong but a > good receiver close to your antenna can pick it up. The frequency will tell > what channel the set is tuned to. (first of all, I'm for the moment *assuming* the above to be true) Seems like they would have trouble picking out stuff coming from one specific tv set, especially in the case of apt/condos where there would be a lot of tv sets going within a small physical area. Also, an antenna amplifier should prevent anything from going back out the antenna. (no I don't have an earth station) -- _____ /_____\ how in blue blazes do they expect a EE to cook on a gas stove? /_______\ |___| Snoopy ____|___|_____ ihnp4!ihuxl!seifert
john@hp-pcd.UUCP (john) (08/09/84)
How to monitor TV reception without busting down doors.
It is possible to determine what station a TV set is tuned to from outside
the house. I have even heard of devices that would let you drive down the
street and figure out what shows people are watching.
The theory is very simple. When you receive a TV station you take the RF
signal from the antenna and mix it with a Local Oscillator signal. The LO
signal is tuned to a frequency that is a fixed amount away from the desired RF
signal. Mixing two signals produces the sum and difference frequencies. The
difference frequency is the "Fixed amount" which now contains all of the signal
information from the original RF signal. The "fixed amount" is also called the
IF frequency and the rest of the TV will work on this signal. Changing channels
is done by tuning the LO to the desired frequency plus or minus the IF
frequency.
Processing a fixed IF signal is less expensive than many RF signals so it
is best (read cheaper) for TV designers to mix the RF and LO as close to the
antenna input as possible. Some of the LO signal may be coupled into the
antenna leads and then broadcast out the antenna. It is not very strong but a
good receiver close to your antenna can pick it up. The frequency will tell
what channel the set is tuned to.
John Eaton
!hplabs!hp-pcd!john